dS-NET I/O Switcher

Overview

The dS-NET-I/O Switcher
provides cascadable 16-into-2 relay switching, and may be used for
switching either analogue or digital (AES3) audio signals
. The I/O Switcher is primarily
intended for use with the dScope Series III test and measurement
system. It is serially-controlled using the Prism Sound
dS–NET
protocol.

Connections

The two 'Bus' connections are each provided on both male and female XLR connectors, allowing each to
be used as either an 'input switcher' (to drive dScope's analyzer
inputs from a selection of many EUT outputs) or an 'output switcher'
(to drive a selection of EUT inputs from the dScope's generator
outputs).

Many I/O Switchers can be cascaded together to make larger input or output switching matrices by
connecting the second XLR connector to a daisy-chain of I/O Switchers.
Alternatively, one of the I/O Switcher's buses can be used as an
8-into-1 input switcher and the other as a 1-into-8 output switcher.

The 16 'channel' connections are provided as two 'Groups' of eight channels, each group on a
25–way female D-sub connector. Breakout cables to XLRs (male for
output switching and female for input switching) are available from
Prism Sound, alternatively the operator can construct his own cable to
suit the EUT. This configuration allows the I/O Switcher to serve as
both input and output switcher without modification, since there is no
need to fit differently-sexed channel XLRs.

Architecture

The crosspoint switching is organised with two Buses ('A' and 'B') and two eight-channel Groups
('X' and 'Y'). Together these form a 16x2 switching matrix. All inputs
and outputs are two-leg balanced connections, although the –ve
(cold) legs can be jumpered to signal ground for unbalanced operation
if required. The crosspoint relays can carry a maximum current of 2A,
and switch a maximum voltage of 250V. Note that repeated switching at
high currents is likely to damage the relay contacts.

Additional features

As well as providing the basic 16-into-2 switching matrix, the I/O Switcher has three additional
functions:

Balance-test mode:

each Bus
can be switched into 'balance-test' mode, a special mode used in the
input switching configuration, for measuring the output balance of the
EUT. In this mode, the Bus output is taken between signal ground and
the centre tap of a 600R resistor connected between the two legs of the
selected input. The resistor is composed of two 0.01% matched halves in
order that the balance of the resistors is unlikely to dominate the
output balance of the equipment under test. The dScope's analyzer input
impedance should be set to 600R in order to enact the standard method
of balance measurement. A maximum signal amplitude of 28dBu (19.45Vrms)
can be tolerated by the balance-test circuit; beyond this, the
resistors may be damaged.

Load switching:

each bus can
be connected to a load applied to a pair of 4mm sockets on the rear of
the I/O Switcher. This is useful for power amplifier testing. The
maximum load current is 12A if the switcher is only connecting the load
to the XLR connector of the Bus, i.e. if the load current does not flow
through the switching matrix. If the load is applied to a Group channel
via the switching matrix, the maximum matrix current of 2A must not be
exceeded. A fuse is included to protect the switching matrix from
excessive currents.

DC measurement:

the DC voltage
on each leg of each bus can be read, in 1V steps, over the
range+/-128V. This is primarily intended for checking phantom power
sourcing from inputs under test.

Serial control

The I/O Switcher's serial control port follows the dS–NET standard, based on the
RS–232
protocol. Up to 64 dS–NET devices can be daisy-chained from
the
dScope's dS–NET connector using special dS–NET
cables.
dS–NET devices are differentiated by setting different
addresses
for each on rear-panel DIP switches. dS–NET devices are
easily
controlled from the dScope's VBScripting system at a high level.

In the case of the
I/O Switcher,
no complex binary manipulations or sequences are required; the desired
channels can be simply selected in a single operation. If multiple
switchers are connected to form large arrays, these can be described at
the head of the script, allowing the whole array to be addressed as if
it were a single switcher. Details of how to control the I/O Switcher
from a VBScript can be found in the dS-NET peripherals section of the
Scripting Manual.

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